Custom Field from KNA1 to add in Business Partner BP using BDT

I have a requirement where I have additional field in KNA1 which I want to bring in BP business Partner. I am working on HANA 1610 system and will use BP to create customer master data.

I created new field group and View containing custom field. I have created FM to pass data from standard Function Group CVI_FS_UI_CUSTOMER to pass data to PBO and PAI of custom screen. I am able to see the additional field in BP and data is getting fetched from the underlying KNA table for the same.

But the problem is I am not able to save the field data to Table KNA1. I know that we have to create FM for DSAVE and XHNG event. But I don't know what codes need to be added in those FM for DSAVE event.